Technical Field
The present embodiments relates to window shading and, more particularly, to window shading systems that incorporate gearing such as involute type gears.
Background Art
In many applications, motor driven window roller shades typically need to be placed with the end of one shade close to the end of another shade to avoid having gaps that can permit light to enter. Therefore, instead of driving each roller shade with its own motor, a single motor is connected to an end of one of the roller shades to directly drive that shade, and an adjoining roller shade is driven by a meshing a gear attached to the other end of the first roller shade with a gear attached to the adjacent end of the next roller shade. In this manner, two or more roller shades may be driven by a single motor.
In some applications, the adjacent roller shades are arranged along a straight line. However, in other applications, each roller shade may be arranged at angle with respect to its adjacent shade. Therefore, each such arrangement could require specific pairs of gears that mesh at angles different than those required by another arrangement. To avoid the cost of making a particular set of gears for each application, it is desirable to provide a pair of gears that can mesh at a range of angles.
Moreover, at the time of installation, there may be minor differences between the angles at which the roller shades are designed to intersect and the actual angles at which they intersect. It is therefore further desirable to provide a pair of gears that are suitable for use in the presence of such differences.
Conventional spur gears have a driving shaft and a driven shaft with a plurality of teeth, respectively, for gearing with each other in parallel so that only the ratio of rotation and the direction of the rotation are changeable. However, the gearing intersection angle of the rotation of the gears is determined when the gears are designed and manufactured. Once the gearing intersection angle is determined, the angle of the rotation cannot change. That is, the gearing intersection angle is not variable.
To provide a variable gearing intersection angle, some prior systems have used a pair of semi-spherical gears. The driving shaft and the driven shaft are each provided with a semi-spherical body member having gear teeth and grooves which are longitudinally and radially arranged so that the gears may engage at any of a range of intersection angles. However, the shape of semi-spherical gears does not permit the ends of the roller shades to be placed sufficiently close to each other. Additionally, the size needed to provide sufficient torque to sequentially drive several roller shades may further increase the size of the gears needed.
Involute gears are some of the most widely used gears in industry. In an involute gear, the profiles of the teeth are involutes of a circle. The contact between two mating involute gear teeth occurs at a single instantaneous point where two involutes of the same spiral hand meet and moves along a fixed plane of contact irrespective of the center-to-center distance of the gears. Thus involute gears can handle center shifts and provide greater assembly flexibility. Moreover, the contact surface between the gears is always perpendicular to the plane of contact, thus helping reduce torque variation.
It is therefore desirable to provide involute gears that can mesh at any angle within a desired range of angles yet are capable of, for example, minimizing the separation between the ends of a pair of motorized roller shades.